1. Field of the Invention
The present invention relates to a multicolor image forming apparatus in which a latent image formed on a photosensitive drum as an image retainer is developed by a plurality of developing means, each of which includes one of multicolor developers, to obtain a color copy using the electrophotographic technique.
2. Prior Art
There have been various methods and apparatus to provide a color image using the electrophotographic technique. According to one method as disclosed in Japanese Patent Laid-Open No. 61-100770, for example, latent images are formed and developed on a photosensitive drum dependent on the number of separated colors of a document image. Whenever each latent image is developed, it is transferred successively onto a transfer drum to form a multicolor image which is then transferred onto a sheet of recording paper to obtain a color copy. An apparatus practicing this method requires, along with the photosensitive drum, the transfer drum which has its circumferential surface enough in size to allow transfer of an image of one sheet onto it. Thus, the apparatus is necessarily increased in dimension and complicated in structure.
In another method as disclosed in Japanese Patent Laid-Open No. 61-149972, latent images are formed and developed on a photosensitive drum dependent on the number of separated colors of a document image. Whenever each latent images is developed, it is transferred successively onto a transfer member to directly obtain a multicolor copy. With this method, difficulty is encountered in superposing images of different colors with high accuracy and a color copy of good quality cannot be obtained.
There is also known a method in which latent images are formed and developed by color toner on a photosensitive drum dependent on the number of separated colors of a document image in a repeated manner, so that powder materials of different colors are superposed on the photosensitive drum and then transferred to obtain a color image.
The basic process of this type multicolor image formation is disclosed in Japanese Patent Laid-Open Nos. 60-75850, 60-76766, 60-95456, 60-95458, and 60-158475 all filed by the applicant.
In the multicolor image forming apparatus which provides a color image using such superposition process, a plurality of developing devices containing therein respective toner of different colors are disposed along the circumference of the photosensitive drum, and the photosensitive drum is usually rotated a plurality of times to successively develop latent images on the photosensitive drum for providing the color image.
The multicolor image forming apparatus having a photosensitive drum, on which images of different colors are superposed, cannot use conventional developing means that includes a magnetic brush brought into the image retainer for development. The applicant made it possible to practice a multicolor image forming apparatus in which toner images are superposed on the image retainer using a non-contact developing technique as disclosed in Japanese Patent Laid-Open No. 57-147652, etc.
For general reproducing machines, as disclosed in Japanese Patent Publication No. 58-54392, it has been proposed to integrally mount a photosensitive drum, a developing device and a cleaner together on a support member for facilitating replacement and repair of respective units. Also, Japanese Patent Laid-Open No. 57-154255 discloses to constitute those components for monocolor copying into an integral structure which is disposable for facilitation of replacement. However, any of those prior arts is not intended to improve quality characteristics of an image, maintainability and serviceability of multicolor image forming apparatus comprising a plurality of developing devices for multicolor or full-color copying.